1904] HOLFERTY: ARCHEGONIUM OF MNIUM 119 
organs. .It is doubtful if we should look upon this as a conver- 
sion of an archegonium into an antheridium, but rather as the 
development of a bisexual organ, or a modified antheridium. 
These cases seem sufficient to establish the homology of 
antheridia and archegonia, and point to their derivation from a 
structure in which eggs and sperms had not yet been differenti- 
ated. Asan illustration, attention may be called to the fact that 
in Selaginella the microsporangia and megasporangia are dif- 
ferentiated from primordia which are doubtless indifferent and 
capable under suitable conditions of producing either kind of 
sporangium. In this case the microsporangium has deviated less 
from the structure of the hypothetical sporangium of the homo- 
sporous ancestor. Mnium furnishes an illustration of an analo- 
gous process, the probably indifferent primordia differentiating 
into antheridia and archegonia, the antheridia deviating less from 
the structure of the hypothetical ancestral gametangium. Here, 
as in Selaginella, the organ which has become most profoundly 
modified contains vestigial structures which indicate its ancestry 
and the method by which it has become modified. 
THE ORIGIN OF THE ARCHEGONIUM. 
The origin of the archegonium and its development into the 
distinct female organ has never been satisfactorily worked out. 
There has been some attempt to relate it to the oogonia of Chara 
or Coleochaete, but no serious claim could now be made for this. 
To derive the bryophyte antheridium from that of some member 
of the Chlorophyceae would seem to be a less difficult task. 
Barnes (16, pp. 277-290) has distinguished between simple 
and compound spermaries and ovaries, using these terms to 
designate sperm-producing and egg-producing organs, the simple 
organs being confined to algae and fungi. The compound 
spermary could be derived from the simple one by the forma- 
tion of walls at the time the sperm cells are organized, and 
by the sterilization of an outer layer of sperm mother-cells for 
protection. The latter process would be a most natural one in 
case the plant was forced to change from an aquatic to a ter- 
restrial habitat. In lectures on the bryophytes at the University 
of Chicago, Barnes has suggested the derivation of the arche- 
